Apparatus for determining the volume of a vessel is known. Such apparatus typically comprises a catheter extending from a proximal end to a distal end and having a plurality of longitudinally spaced apart electrodes located towards the distal end of the catheter. Two of the electrodes, namely, the two extreme electrodes, typically are stimulating electrodes for receiving a stimulus signal, while the remaining electrodes which are located between the stimulating electrodes are sensing electrodes on which a voltage develops in response to the stimulus signal when the catheter is located in a vessel containing an electrically conductive medium. By providing the stimulus signal as a constant current signal of known current value, and by determining the voltages developed on the sensing electrodes, a determination of the volume of the vessel can be made.
Where it is not feasible to provide an electrically conductive medium in the vessel, the volume of which is to be determined, a balloon catheter is provided whereby a balloon is located on the end of the catheter with the catheter extending through the balloon. The stimulating and sensing electrodes are located on the catheter within the balloon. The balloon is inserted into the vessel the volume of which is to be determined and inflated with an electrically conductive inflating medium. The balloon typically is inflated to fill the vessel, so that the balloon when inflated defines the interior of the vessel. With the balloon defining the interior of the vessel, a stimulus signal is applied to the stimulating electrodes, and resulting voltages on the sensing electrodes are simultaneously read. The volume of the inflated balloon and in turn the volume of the vessel is computed from the read values of the voltages on the sensing electrodes, the value of the current applied to the stimulating electrodes and the electrical resistance of the inflating medium.
However, a problem with such apparatus known heretofore is that it is not possible to determine the volume of a part of the vessel, and additionally, in the case of apparatus which comprise a balloon catheter, it is difficult and in many cases impossible to determine when the balloon has been inflated to a state where it defines the interior of the vessel, since inflating of the balloon may also cause the vessel, the volume of which is to be determined to expand.
There is therefore a need for a method and apparatus for determining volume of a vessel which addresses these problems.
The invention is directed towards a method and apparatus for determining volume of a vessel, and the invention is also directed towards a method and apparatus for determining volume of a part of a vessel, for example, a pouch formed in a stomach during bariatric surgery.